for a list of ballpark current draw for some common taper gear. Some specs list the current draw, others may require calculating:

Current (amps) = Power (watts) / Voltage (volts)

If you know the capacity of the battery and the current draw of the gear, it's just simple division to figure out the run time:

( Battery Capacity [mAH] / Current Draw [mA] ) * ( .80 )

Note: A good rule of thumb is to only assume 80% efficiency. So multiply by .80 since you don't want to run your battery completely down - this will shorten it's life if it's an SLA. Additionally, most AH ratings are determined using a slower draw than most of our gear, and batteries are not as efficient at faster draws. So, conservatively assume you'll only use 80% of the battery capacity. (NiMH batteries will likely get higher than 80% efficiency, but never hurts to estimate a bit conservatively.)